1. Field of the Invention
The present invention relates generally to flat panel displays (FPDs), and more specifically to field emission displays (FEDs) and grating light valves (GLVs). Even more specifically, the present invention relates to the cathode structure of a field emission display (FED).
2. Discussion of the Related Art
A field emission display (FED) is a low power, flat cathode ray tube type display that uses a matrix-addressed cold cathode to produce light from a screen coated with phosphor materials. FIG. 1 is a side cut-away (cross sectional) view of a conventional FED. The FED 100 includes a cathode plate 102 and an anode plate 104 (or face plate), which opposes the cathode plate 102. The cathode plate 102 includes a cathode substrate 106, cathode electrodes (cathode electrode 107 is illustrated) printed on the substrate 106, a dielectric layer 108 disposed on the cathode substrate 106 and the cathode electrode 107, and a gate electrode 114 disposed on the dielectric layer 108 and several emitter wells 110 formed within the gate electrode 114 and the dielectric layer 108. An electron emitter 112 is deposited within each emitter well 110, the emitters 112 shaped as conical electron emitters, e.g., Spindt tips.
The anode plate 104 includes a transparent substrate 116 (face plate or display face) upon which is formed various phosphors (e.g., red, green and blue) that oppose the electron emitters 112, for example, a red phosphor 120 is illustrated. A thin metallic anode 118 is formed over the phosphors, e.g., phosphor 120.
It is important that the cathode plate 102 and the opposed anode plate 104 be maintained insulated from one another at a relatively small, but uniform distance from one another throughout the full extent of the display face in order to prevent electrical breakdown between the cathode plate and the anode plate, provide a desired thinness, and to provide uniform resolution and brightness. Additionally, in order to allow free flow of electrons from the cathode plate 102 to the phosphors and to prevent chemical contamination, the cathode plate 102 and the anode plate 104 are sealed within a vacuum. In order to maintain a uniform separation between the cathode plate 102 and the anode plate 104 across the dimensions of the FED in the pressure of the vacuum, structurally rigid spacers (not shown) are positioned between the cathode plate 102 and the anode plate 104.
The FED 100 operates by selectively applying a voltage potential between the cathode electrode 107 and the gate electrode 114, producing an electric field 122 focused to cause a selective electron emission 124 from the tips of the electron emitters 112. The emitted electrons are accelerated toward and illuminate the phosphor 120 of the anode 118 by applying a proper potential to the anode 118. The anode potential must be high enough that the electrons penetrate through the anode 118 to illuminate the phosphors. One problem with known FEDs is that a high electric field is necessary to drive the device. Thus, designers use a very high drive voltage or use sub-micron spacing between the cathode electrode 107 and the gate electrode 114, which may lead to crosstalk and increases the cost of the FED.
A grating light valve (GLV) is micromachined diffraction grating that acts as a spatial light modulator (SLM) to vary how light is reflected from each of multiple deflecting ribbon-like structures and are commonly used projection elements. A conventional GLV 10, such as described in U.S. Pat. No. 5,311,360, issued May 10, 1994 to Bloom et al., entitled METHOD AND APPARATUS FOR MODULATING A LIGHT BEAM, is illustrated in FIGS. 2, 3 and 4. A pattern of deformable elements 18 (typically ribbons) are formed in a spaced relationship over a substrate 16 having an electrode 24 formed on the base of the substrate 16. The elements 18 and the substrate 16 are coated with a reflective material 22. In FIG. 3, the grating 10 is shown in a non-diffracting state with no voltage applied between the electrode 24 of the substrate 16 and the individual elements 18, and with a lightwave 26 incident upon it. The height difference between the reflective material 22 on the elements 18 and on the substrate 16 is designed to be xcex/2 of the incident lightwave 26 when the deformable elements 18 are in a relaxed state (FIG. 3), such that light reflected from the elements 18 and from the substrate 16 add in phase and the grating 10 acts to reflect the incident lightwave 26 as a flat mirror.
However, as illustrated in FIG. 4, when a voltage is applied between the elements 18 and the electrode 24 of the substrate 16, the electrostatic forces pull the elements 18 down onto the substrate 16, with the result that the distance between the top of the elements 18 and the top of the substrate 16 is now xcex/4 of the incident lightwave 26. Thus, the total path length difference for the light reflected from the elements 18 and from the substrate 16 is now xcex/2 of the incident lightwave and the reflections interfere destructively, causing the light to be diffracted, indicated as 28. By using this grating 10 in combination with a system, for detecting the reflected light, which has a numerical aperture sized to detect one order of diffracted light from the grating, the grating 10 can used to be modulate the reflected light with high contrast in order to create a projection display.
Typically, the elements 18 are formed by depositing a layer of conducting material over an insulating layer 11 formed on a substrate, then etching away the elements 18 and portions of the insulating layer 11 such that the remaining portions of the conducting material form the elements 18. However, the entire conducting layer is not etched away, in order to form a frame 20 that the elements 18 are tensioned between and which is supported above the substrate 16 by the remaining portions of the insulating layer 11.
The invention provides an electron emitting structure that uses a field emission display (FED)-like cathode in combination with deflecting electrodes or deflecting ribbons, such as used in grating light valves (GLVS) to produce various electron emitting structures. In a preferred form, the electron emitting structure is used as a cathode plate of an FED, which advantageously, provides lower drive voltages in order to provide an electric field sufficient to produce an electron emission without requiring sub-micron spacing between electrodes.
In one embodiment, the invention can be characterized as an electron emitting structure comprising a substrate having base electrodes and gate electrodes coupled thereto, an insulating material separating and electrically insulating the base electrodes and the gate electrodes, and an electron emitting material deposited on active regions of the base electrodes. Upon applying a voltage potential difference between a respective base electrode and a respective gate electrode, a portion of one of the respective base electrode and the respective gate electrode deflects through electrostatic force positioning the portion of the one of the respective base electrode and the respective gate electrode relative to another one of the respective base electrode and the respective gate electrode such that an electric field is produced at a respective active region sufficient to cause an electron emission from a respective electron emitting material deposited on the respective active region.
In another embodiment, the invention can be characterized as a method of electron emission comprising the steps of: applying a voltage potential difference between a base electrode and a gate electrode of an electron emitting structure, the base electrode electrically insulated from the gate electrode; deflecting, as a result of the applying step, a portion of one of the base electrode and the gate electrode to position the portion of the one of the base electrode and the gate electrode relative to another one of the base electrode and the gate electrode; and producing, as a result of the applying and deflecting steps, an electric field at an active region of the base electrode sufficient to cause an electron emission from an electron emitting material on the active region.
In a further embodiment, the invention may be characterized as a field emission display comprising a cathode plate and an anode plate. The cathode plate comprises a substrate having base electrodes and gate electrodes coupled thereto, an insulating material separating and electrically insulating the base electrodes and the gate electrodes, and an electron emitting material deposited on active sub-pixel regions of the base electrodes. Upon applying a voltage potential difference between a respective base electrode and a respective pair of gate electrodes, a portion of one of the respective base electrode and the respective pair of gate electrodes deflects through electrostatic force positioning the portion of the one of the respective base electrode and the respective pair of gate electrodes relative to another one of the respective base electrode and the respective pair of gate electrodes such that an electric field is produced at a respective active region sufficient to cause an electron emission from a respective electron emitting material deposited on the respective active region. The anode plate comprises a transparent substrate separated above the cathode plate and phosphor material coupled to the transparent substrate, portions of the phosphor material corresponding to active sub-pixel regions of the base electrodes, the electron emission illuminating a respective portion of the phosphor material.